Aim -The main focus of the project was to identify whether there is any interaction between Ketotifen Fumarate (antihistamine) and domperidone (Antiemetic/dopaminergic antagonist) present or not at simulated gastric and intestinal solutions of different pH. Methods -Using Job's continuous-variation analysis the possible drug-drug interaction was determined at a fixed temperature (37ºC) at the studied pH. From Job's continuous-variation analysis the views of drug-drug interaction at different concentration ratio at all pH (0.4, 1.2, 2.0, 2.8, 6.8, and 7.4) except 6.0 were noted. Results -Data obtained from spectroscopic analysis showed decrease in free-drug concentration of both of the drugs analyzed when they were within the same gastric simulated solution. Conclusion -Concurrent administration of Ketotifen Fumarate and domperidone would result in the formation of a stable complex and this is likely to reduce the the rapeutic activities of both drugs.